The invention relates to the separation of a shaped substrate from a stamping tool having a pair of chamber parts, which can move with respect to one another, of a closeable chamber, of which a first chamber part serves as a support for the stamping tool and a second chamber part serves as a support for the shapeable substrate.
A method for producing microengineered components is known under the name of LIGA process (LIGA is a German acronym for Lithography with Synchrotron Radiation, Electroplating, Molding using plastics). By pressing a molding tool into a moldable material, such as for example a layer of thermoplastic, three-dimensional patterns with heights in the range from a few nanometers to a few hundred micrometers are produced, preferably under vacuum and at a temperature which lies above the softening temperature of the moldable material.
A device in accordance with DE 196 48 844 C1 which is suitable for this purpose contains a chamber with one chamber part fixed to the frame and one moveable chamber part. Setting the pressure and temperature conditions inside the chamber is linked to predetermined values of a force acting on the fixed chamber part.
After the hot-molding process has finished, the moldable material which has been applied to a substrate support on the fixed chamber part adheres to the patterns of the molding tool due to large aspect ratios, shrinkage processes and surface roughness of the molding tool caused by the process, and has to be separated in a suitable manner.
A device in accordance with DE 195 09 452 A1, which is intended to keep flexural stresses at a low level during demolding and to avoid geometric limitations on the molding-tool surface available is used for this demolding.
A mold insert whose microstructure is transferred to a molded part is surrounded, in its edge area, by an ejector which, in order to demold the molded part, can be moved between an at-rest position and a working position. A space which can be filled with a pressurized fluid is provided on that side of the ejector which is remote from the molded part. In the working position of the ejector, the intention is that the fluid should act beneath the edges of the molded part, build up a pressure between the mold insert and the molded part which is to be demolded and, as a result, assist with demolding. Moreover, it is intended that the ejector be moved into its working position with the aid of the pressure from the fluid.
However, in the solution disclosed a method of operation of this nature, in which the space provided for the dual function of the fluid has to be designed as a pressure chamber and, in order to displace the ejector, has to act as a pneumatic cylinder, involves considerable unreliability. This is because the mold insert and the adjoining ejector, together with the layer of the molded part lying above it, are provided as wall elements of the space. The undefined adhesion of the molded part on the ejector may lead to unsealed areas and may have a considerable adverse effect on the function of the device.
Also, the control of the demolding process is undefined, both as a result of the force control applied and the termination by means of mechanical stops. The behavior of the shaped part remains largely uncontrollable.
A further drawback is the edge-side matching of the ejector to the mold insert, since such a direct interface with an expensive component unnecessarily increases the risk of damage or of some other adverse effect on the tool.
The primary object of the invention is to make demolding more operationally reliable and to largely prevent damage to expensive components.
According to the invention, the object is achieved by means of a device for separating a shaped substrate from a stamping tool having a pair of chamber parts, which can be moved with respect to one another, of a closeable chamber, of which a first chamber part serves as a support for the stamping tool and a second chamber part serves as a support for the shapeable substrate. The chamber contains a substrate holder which, when the chamber is closed, fixes the substrate to its support outside the stamping area, with the result that the substrate is detached from the stamping tool when the chamber is opened.
Furthermore, the substrate holder can be displaced parallel to the direction of movement of the chamber parts and, together with the support for the stamping tool, encloses a first pressure chamber. Advantageously, the first pressure chamber is machined into the support for the stamping tool as an annular groove which the substrate holder delimits.
The pressure chamber contains the substrate holder as a moveable part and operates, with a high level of reliability, as a pneumatic cylinder with which the substrate holder is moved towards the substrate by increasing the volume of the chamber.
It is also advantageous if the substrate holder surrounds a tool holder on the support for the stamping tool, which tool holder engages around the peripheral face of the stamping tool. This avoids a direct interface between the expensive stamping tool and a moveable part, thus considerably reducing the risk of damage.
Furthermore, the substrate holder, where it rests on the substrate, delimits, together with the tool holder, a second pressure chamber, into which at least one duct for compressed air is guided, through the tool holder, in order to assist with detaching the substrate from the stamping tool when the chamber is opened.
The support for the stamping tool contains feed ducts for compressed air, a first of which ducts is connected to the first pressure chamber and a second of which ducts is connected to the duct in the tool holder.
Moreover, the invention also relates to a method for separating a shaped substrate from a stamping tool inside a closed chamber which contains a pair of chamber parts which can move with respect to one another, of which a first chamber part serves as a support for the stamping tool and a second chamber part serves as a support for the shapeable substrate. The substrate is fixed to its support in an edge area which lies outside a stamping area and is detached from the stamping tool by opening the chamber.
It is advantageous if an initial detachment area which is formed in the fixed edge area when the chamber is opened is increased in size by means of compressed air and further opening of the chamber until the substrate is completely separated from the stamping tool.
In contrast to the known solution in accordance with DE 195 09 452 A1, in which the molded part is detached from the mold insert in functional terms only by means of force control by way of the ejector, the detachment of the substrate from the stamping tool is divided into various functional sequences which can be controlled differently. While the substrate is held to its support in the edge area, it is possible to separate it from the stamping tool by suitably regulating the opening of the chamber. The performance of the molded part remains largely controllable. The substrate is not stripped off or ejected, but rather is initially held in place and is then pulled off.
For the functional sequences which can be carried out by means of compressed air, separate pressure chambers are provided, in which stable pressure conditions prevail at any time. Advantageously, the detachment operation can at any time be reliably controlled in such a way that the moldable material is removed evenly, without spring-back effects and without tearing off patterns from the tool. The avoidance of manual rework, together with the possibility of automating the separate process steps which can be reproduced subsequent to molding, lead to an increase in productivity.
The invention is to be explained in more detail below with reference to the diagrammatic drawings.